Bottom Line:
Interestingly, in the gip1Delta mutant, not only is Glc7p localization altered, but septins are also delocalized.Similar phenotypes were observed in a glc7-136 mutant, which expresses a Glc7p defective in interacting with Gip1p.These results indicate that a Gip1p-Glc7p phosphatase complex is required for proper septin organization and initiation of spore wall formation during sporulation.

Affiliation: Department of Biochemistry and Cell Biology, Institute for Cell and Developmental Biology, State University of New York at Stony Brook, Stony Brook, NY 11794, USA.

ABSTRACTSporulation of Saccharomyces cerevisiae is a developmental process in which a single cell is converted into four haploid spores. GIP1, encoding a developmentally regulated protein phosphatase 1 interacting protein, is required for spore formation. Here we show that GIP1 and the protein phosphatase 1 encoded by GLC7 play essential roles in spore development. The gip1Delta mutant undergoes meiosis and prospore membrane formation normally, but is specifically defective in spore wall synthesis. We demonstrate that in wild-type cells, distinct layers of the spore wall are deposited in a specific temporal order, and that gip1Delta cells display a discrete arrest at the onset of spore wall deposition. Localization studies revealed that Gip1p and Glc7p colocalize with the septins in structures underlying the growing prospore membranes. Interestingly, in the gip1Delta mutant, not only is Glc7p localization altered, but septins are also delocalized. Similar phenotypes were observed in a glc7-136 mutant, which expresses a Glc7p defective in interacting with Gip1p. These results indicate that a Gip1p-Glc7p phosphatase complex is required for proper septin organization and initiation of spore wall formation during sporulation.

fig10: glc7–136 mutants show a similar phenotype to the gip1Δ mutant. (A) SB247 (glc7–136/glc7–136) at a late stage of sporulation was analyzed by transmission EM. Prospore membranes (PrM) and nucleus (N) are indicated. (B–I) NY527 (glc7–136/glc7–136) harboring either pCEN-SPR28-GFP or 2 μ HA-GIP1 was sporulated and analyzed by fluorescence microscopy. (B and D) anti-GFP staining; (C and E) DAPI staining of cells in B and D, respectively; (F and H) Anti-HA staining; (G and I) DAPI staining of cells in F and H, respectively. Bar, 500 nm.

Mentions:
To determine whether the phenotypes of the gip1Δ mutant are caused by a failure to properly localize Glc7p or a second function of the Gip1 protein, we examined the sporulation phenotype of a strain carrying the glc7–136 allele. The glc7–136 mutant causes a sporulation defect (Baker et al., 1997), and the protein is defective in interaction with Gip1p (unpublished data). Thus, if the sporulation defect of the gip1Δ mutant is due to altered localization of Glc7p, the glc7–136 mutant should display similar phenotypes. EM analysis of SB247, a glc7–136 mutant in the JC482 background (Baker et al., 1997), was performed. The cytological phenotype of glc7–136 was more heterogeneous than gip1Δ, probably due to the leaky sporulation defect of the mutant (2% asci). Nonetheless, a significant fraction of the cells (50%) displayed prospores with no apparent deposition of spore wall material (Fig. 10 A), similar to the gip1Δ mutant (Fig. 2). Thus, glc7–136 mutant cells display a block to spore wall deposition similar to that seen in the gip1 deletion strain.

fig10: glc7–136 mutants show a similar phenotype to the gip1Δ mutant. (A) SB247 (glc7–136/glc7–136) at a late stage of sporulation was analyzed by transmission EM. Prospore membranes (PrM) and nucleus (N) are indicated. (B–I) NY527 (glc7–136/glc7–136) harboring either pCEN-SPR28-GFP or 2 μ HA-GIP1 was sporulated and analyzed by fluorescence microscopy. (B and D) anti-GFP staining; (C and E) DAPI staining of cells in B and D, respectively; (F and H) Anti-HA staining; (G and I) DAPI staining of cells in F and H, respectively. Bar, 500 nm.

Mentions:
To determine whether the phenotypes of the gip1Δ mutant are caused by a failure to properly localize Glc7p or a second function of the Gip1 protein, we examined the sporulation phenotype of a strain carrying the glc7–136 allele. The glc7–136 mutant causes a sporulation defect (Baker et al., 1997), and the protein is defective in interaction with Gip1p (unpublished data). Thus, if the sporulation defect of the gip1Δ mutant is due to altered localization of Glc7p, the glc7–136 mutant should display similar phenotypes. EM analysis of SB247, a glc7–136 mutant in the JC482 background (Baker et al., 1997), was performed. The cytological phenotype of glc7–136 was more heterogeneous than gip1Δ, probably due to the leaky sporulation defect of the mutant (2% asci). Nonetheless, a significant fraction of the cells (50%) displayed prospores with no apparent deposition of spore wall material (Fig. 10 A), similar to the gip1Δ mutant (Fig. 2). Thus, glc7–136 mutant cells display a block to spore wall deposition similar to that seen in the gip1 deletion strain.

Bottom Line:
Interestingly, in the gip1Delta mutant, not only is Glc7p localization altered, but septins are also delocalized.Similar phenotypes were observed in a glc7-136 mutant, which expresses a Glc7p defective in interacting with Gip1p.These results indicate that a Gip1p-Glc7p phosphatase complex is required for proper septin organization and initiation of spore wall formation during sporulation.

Affiliation:
Department of Biochemistry and Cell Biology, Institute for Cell and Developmental Biology, State University of New York at Stony Brook, Stony Brook, NY 11794, USA.

ABSTRACTSporulation of Saccharomyces cerevisiae is a developmental process in which a single cell is converted into four haploid spores. GIP1, encoding a developmentally regulated protein phosphatase 1 interacting protein, is required for spore formation. Here we show that GIP1 and the protein phosphatase 1 encoded by GLC7 play essential roles in spore development. The gip1Delta mutant undergoes meiosis and prospore membrane formation normally, but is specifically defective in spore wall synthesis. We demonstrate that in wild-type cells, distinct layers of the spore wall are deposited in a specific temporal order, and that gip1Delta cells display a discrete arrest at the onset of spore wall deposition. Localization studies revealed that Gip1p and Glc7p colocalize with the septins in structures underlying the growing prospore membranes. Interestingly, in the gip1Delta mutant, not only is Glc7p localization altered, but septins are also delocalized. Similar phenotypes were observed in a glc7-136 mutant, which expresses a Glc7p defective in interacting with Gip1p. These results indicate that a Gip1p-Glc7p phosphatase complex is required for proper septin organization and initiation of spore wall formation during sporulation.